1. Field of the Invention
The present invention relates generally to wireless communications and, more particularly, to a space-time and channel coding modulation scheme for use in wireless communication systems.
2. Background Information
As mobile radio-based communication becomes more widely accepted, it will be desirable to provide various types of radio-based communication services to meet consumer demand. For example, support for facsimile, e-mail, video, Internet access, and the like via radio-based communication systems is envisioned. Moreover, it is expected that mobile users may wish to access different types of services at the same time. For example, a video-conference between two mobile users would involve both speech and video support. Some of these different services will require relatively high data rates compared with speech service that has been conventionally supplied by mobile radio-based communication systems. Accordingly, next generation mobile radio-based communication systems are being designed to provide the high and variable-rate data rate communication bandwidth required by such services.
One such next or “third” generation radio-based communication system, termed the Universal Mobile Telecommunications System (UMTS), has been proposed by the Third Generation Partnership Project (3GPP). The 3GPP is comprised of various standard setting bodies, which have jointly endeavored to produce globally applicable technical specifications and technical reports for the UMTS. Although the UMTS defines a unique specification for radio-based communication, it is based on evolved Global System for Mobile Communications (GSM) core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access Network (UTRAN) including both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). It is anticipated that mobile radio-based communication networks compliant with the specifications of the UMTS will possess sufficient bandwidth to support the advanced services envisioned for third generation communication systems.
In view of the bandwidth requirements of the UMTS and other next generation cellular systems, utilization of advanced multidimensional modulation schemes may be considered. In the case of code division multiple access (CDMA) systems, for example, this may involve transitioning from the use of BPSK/QPSK modulation techniques to multi-dimensional modulation (e.g. multi-dimensional Q2PSK).
It is anticipated that transitions such as this will rely heavily on the use of trellis coded modulation (TCM) and turbo trellis coding techniques. TCM has evolved over the past two decades as a combined coding and modulation technique for digital transmission over band-limited channels. TCM offers a significant advantages relative to classical coding schemes in both power and bandwidth efficiency. In operation, TCM schemes use redundant non-binary modulation in combination with a finite-state encoder that determines a corresponding signal shape to be transmitted over the applicable channel. At the receiver, the received signals are decoded by a soft-decision maximum-likelihood (ML) Viterbi or maximum a posteriori (MAP) decoder. It has been reported that simple four-state TCM schemes can improve the robustness of digital transmission against additive noise (i.e., the “coding gain”) by 3 dB relative to conventional, uncoded modulation. With more complex TCM schemes the coding gain can reach 6 dB or more.